An increasing number of automobiles have air bag crash systems. The air bag is typically located on the steering wheel facing the driver. The air bag must be in continuous electrical connection with impact sensors in the car body. In the event of a crash, the impact sensor or sensors provide an electrical signal to the air bag crash assembly that instantly inflates the air bag. Accordingly, there is an essential need for a reliable electrical connection between the rotatable portion of the air bag assembly, which is mounted to the steering wheel, and the remaining portion of the assembly, which is mounted to the stationary steering column.
Electrical connections between rotatable and stationary parts are well-known. Typically, an electrical brush rests upon a conductive ring, with one of the parts being rotatable to provide a rotatable electrical connection. However, there is a risk, particularly during the impact of an accident, of transient failure of the electrical connection in the brush and ring system, which could result in failure of the entire air bag system crash assembly.
Accordingly, a clockspring has been previously developed. The clockspring typically includes a flat, flexible ribbon cable wound around a rotatable hub. The rotatable hub is located on the steering column. The ribbon cable is contained within a housing. A first end of the ribbon cable is connected to a deployment unit of the air bag and a second end of the ribbon cable is connected to interconnectors which pass out of the housing. The interconnectors are connected to the impact sensor or sensors on a stationary location of the vehicle. In this manner, the deployment unit for the air bag is reliably connected to the impact sensors of the vehicle.
One of the drawbacks to clocksprings using coiled flat connector cables, or ribbon tapes, is that the steering column must have a "center" position. The clockspring must be mounted on the steering column when it is in it's centered position. This is to prevent the ribbon tape from "running out" if the driver makes a large turn of the steering wheel to the left or the right. Running out of ribbon tape is an inherent problem with clocksprings for steering columns.
Another problem with conventional clocksprings is noise generated by the flat connector cables. When a driver turns the steering wheel with a conventional clockspring to the left or the right, the flat connector cable uncoils or coils up within the steering column. This coiling or uncoiling inevitably produces an audible noise that can be heard by the driver. As consumers become more and more demanding of comfort concerns in their vehicle, undesirable or unpleasant noises are considered unacceptable aspects for vehicle manufacturers.
Following the same theme of customer comfort, more and more vehicle controls are being placed upon the steering wheel. Since modern vehicles typically include airbag systems, the clockspring utilized for the airbag system must also accommodate the electrical connections for vehicle controls. Some of these vehicle controls include turn signals, windshield wipers, lights, cruise, defrost, defog, and horn. Even circuitry for powering a heating element in the steering wheel is being included in the clockspring. Accordingly, more and more electrical connections are being communicated through the clockspring. In a conventional clockspring, this requires more and more individual electrical wires to be crammed into the flat connector cable. A greater number of individual wires in the flat connector cable decreases the flexibility of the cable, and increases the noise generated by coiling and uncoiling a stiffer a cable.
Not only are more features being added to the steering wheel, but devices and controls having higher current demands are also being added. For example, one such feature is a heating element in the steering wheel. A conventional clockspring is not designed to handle such a high current device. Since clocksprings typically utilize thin ribbon cables with low amperage wiring, it can be potentially dangerous for high currents to flow through clocksprings. An uncontrolled high current in a clockspring could damage the vehicle and its instruments. Furthermore, resulting damage to the clockspring could likely defeat a major purpose of the clockspring: providing a reliable electrical connection for the airbag safety system. Moreover, such an uncontrolled current could cause a fire damaging the vehicle and seriously injuring a driver or a passenger.
Accordingly, there is a need for a clockspring design that eliminates the need for a centering position, eliminates the risks of over turning the clockspring, increases the available number individual circuit connections, increases the current load tolerance, and also reduces any noise generated by rotating the clockspring.